Soil‐pot tests with iron‐deficiency susceptible soybeans and other plants to determine effectiveness of iron chelates in plant nutrition

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Abstract
The Fe‐inefficient PI54619–5–1 soybean (Glycine max L.) is useful in the assessment of effectiveness of Fe‐containing chemicals for the correction of Fe deficiency in plants. For routine tests, germinated seedlings are transferred to 500‐g quantities of a calcareous soil and the Fe amendments are added in soluble form. Most information is obtained when soils of two different pH values are used such as pH 7.3 and 8.2 each ± 0.3. Nitrogen at 100 to 200 ppm of soil and as NH4 NO3 is also applied. Responses are apparent within 3 to 5 days and leaf analyses are made after about 2 weeks. The addition of 1/2% MgCO3 or less with thorough mixing into noncalcarcous soil has resulted in Fe deficiency not only for this soybean variety, but also for other plant species. An experiment of six replications × 2 soil pH × 7 treatments = 84 pots allows for reasonable statistical evaluations of yields and mineral composition of leaves. A visual comparison of leaf color is recorded and yields of shoots are determined. Analytical data for micronutrients and P, K, Ca, Mg, and Na arc obtained by emission spectrography and these are useful in the interpretation of results when computed upon both a percent of dry weight or per plant basis. Useful compounds are effective at 2 ppm Fe or less in the soil. Tests with bush beans (Phaseolus vulgaris L. var Improved Tendergreen) which are efficient in Fe uptake are useful also because comparison can be made without complications due to differences in plant yields. Comparative effectiveness of two somewhat similar Fe chelates was tested with Fe‐efficient bush beans (Phaseolus vulgaris L. var Improved Tendergreen) in Fe‐sufficient soil. One chelate was FeEDDHA (ethylenediamine di(o‐hydroxyphenylacetic acid) and the oilier was also a phenolic compound, but with slightly different structure. Results in terms of Fe levels in the leaves of the plants were similar at 1/2, 1, and 2 ppm Fe in soil, but the FeEDDHA was somewhat superior at 4 ppm Fe.